Radial and axial bearings are used to support a turret on a vessel, for example a floating production, storage and offloading (FPSO) vessel or a floating storage and offloading (FSO) vessel. The FPSO/FSO vessel can be moored using a turret mooring system in which a fixed turret column is held by an internal or external vessel structure using a bearing arrangement. The vessel-bound components can weathervane freely around the turret, which is fixed via a number of anchor lines with respect to the seabed. This arrangement allows the vessel to adopt the direction of least resistance against wind, current, and wave influences.
When harsh wind and/or waves impact a FPSO/FSO vessel, the turret is pressed against the radial and axial turret bearings. Furthermore, the vessel's hull bends in various ways, such as hogging and sagging. To deal with this bending, some kind of flexibility can be introduced into the bearing system to ensure that the load is distributed among many wheels rather than overloaded onto one or two wheels. A known design is to mount and spring-load wheels, as described in U.S. Pat. No. 5,860,382. The described structure has a spring-loaded wheel in a box assembly, with a spring rod fixed horizontally and vertically to the box assembly. Outer guiding of the box assembly is done by brackets or slots in the surrounding ship structure, or with large steel sections around the rotatable turret rail. The spring rod is fastened to a lid that has to be bolted to the surrounding structure. This type of arrangement uses a fine alignment between the box assembly and the spring rod, and also has fine tolerances in the surrounding structure. The radial loads go through the lid bolts, even when the springs are totally compressed and extreme stemming loads occur.
Improvements in spring-loaded wheel bearings are described in International Patent App. Pub. No. WO 2014/172570, incorporated by reference herein, which discusses cartridge-installable radial bearing sub-assemblies having spring systems configured to pass large radial forces into a vessel's supporting structure. Additionally or alternatively, U.S. Pat. No. 7,063,032 discusses a bearing assembly having sufficiently long vertical support beams so that a lower portion of the bearing support assembly can be connected to the vessel near the vertical center of the vessel in order to minimize deflections of the bearing assembly due to hogging or sagging of the vessel.